1. Field of the Invention
The present invention generally relates to contacts for integrated circuit devices and more particularly to improved landing pads for contacts for self-aligned sidewall image conductors.
2. Description of the Related Art
Sidewall Image Transfer (SIT) techniques form conductors with very narrow widths or semiconductor devices with very short gate lengths without using critical photolithography. For example, a top view of a contact opening 10 for a sidewall conductor 11 is shown in FIG. 1A and cross-sectional views at different points along the same structure are shown in FIGS. 1B and 1C. More specifically, FIG. 1B is a cross-section of FIG. 1A along line A-A′ and FIG. 1C is a cross-section of FIG. 1A along line B-B′.
In sidewall image transfer technology, conductive sidewalls 11 are formed adjacent an insulating mandrel 12. More specifically, the insulator 12 (such as a glass or oxide) is formed using conventional lithographic techniques including depositing and patterning. The sidewall spacer conductors 11 are formed using conventional deposition and directional etching techniques (e.g., reactive ion etching—RIE), as is well known to those ordinarily skilled in the art. More specifically, a conductor (such as metal, alloy or polysilicon) is deposited to surround and cover the insulator 12. Then, a directional etch is applied to the conductor. The directional etch removes material from horizontal surfaces at a much faster rate that it removes material from vertical surfaces, thereby leaving sidewall spacers 11, as shown in FIG. 1B. The directional etch could be, for example, a reactive ion etching process which is selective to the conductor and does not affect the insulator 12 or the underlying substrate.
The insulator 12 can be formed to have a minimum lithographic size which allows the conductive spacers 11 to be formed at sub-lithographic sizes. FIG. 1A also illustrates trim areas 13 which will eventually be removed to permit separation of the distinct conductors 11.
Openings 10 into an insulator 14 are made using standard lithographic or other similar techniques. The openings 10 will eventually be filled with a conductive material to allow contact to an upper layer of wiring which will be formed at a later processing step.
However, the contact opening 10 must be small because the sidewall conductor 11 is very narrow (e.g., possibly sub-lithographic). This makes the alignment and overlay process very difficult, which in turn decreases yield and imposes limits on the pitch of structures so formed. Therefore, there is in a need for an improved structure and system for forming contacts to sidewall image transfer conductors.